WO2021173396A1 - Communication de données sensibles dans un canal de données restreint - Google Patents

Communication de données sensibles dans un canal de données restreint Download PDF

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Publication number
WO2021173396A1
WO2021173396A1 PCT/US2021/018344 US2021018344W WO2021173396A1 WO 2021173396 A1 WO2021173396 A1 WO 2021173396A1 US 2021018344 W US2021018344 W US 2021018344W WO 2021173396 A1 WO2021173396 A1 WO 2021173396A1
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WIPO (PCT)
Prior art keywords
transaction
event
elements
data
information
Prior art date
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PCT/US2021/018344
Other languages
English (en)
Inventor
Mehdi Collinge
Omar Laazimani
Alan Johnson
Original Assignee
Mastercard International Incorporated
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
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Publication date
Application filed by Mastercard International Incorporated filed Critical Mastercard International Incorporated
Priority to US17/802,515 priority Critical patent/US20230164122A1/en
Priority to CN202180017279.2A priority patent/CN115191102A/zh
Publication of WO2021173396A1 publication Critical patent/WO2021173396A1/fr

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Classifications

    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06Q—INFORMATION AND COMMUNICATION TECHNOLOGY [ICT] SPECIALLY ADAPTED FOR ADMINISTRATIVE, COMMERCIAL, FINANCIAL, MANAGERIAL OR SUPERVISORY PURPOSES; SYSTEMS OR METHODS SPECIALLY ADAPTED FOR ADMINISTRATIVE, COMMERCIAL, FINANCIAL, MANAGERIAL OR SUPERVISORY PURPOSES, NOT OTHERWISE PROVIDED FOR
    • G06Q20/00—Payment architectures, schemes or protocols
    • G06Q20/38—Payment protocols; Details thereof
    • G06Q20/382—Payment protocols; Details thereof insuring higher security of transaction
    • G06Q20/3821—Electronic credentials
    • G06Q20/38215—Use of certificates or encrypted proofs of transaction rights
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L63/00—Network architectures or network communication protocols for network security
    • H04L63/04—Network architectures or network communication protocols for network security for providing a confidential data exchange among entities communicating through data packet networks
    • H04L63/0428—Network architectures or network communication protocols for network security for providing a confidential data exchange among entities communicating through data packet networks wherein the data content is protected, e.g. by encrypting or encapsulating the payload
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06Q—INFORMATION AND COMMUNICATION TECHNOLOGY [ICT] SPECIALLY ADAPTED FOR ADMINISTRATIVE, COMMERCIAL, FINANCIAL, MANAGERIAL OR SUPERVISORY PURPOSES; SYSTEMS OR METHODS SPECIALLY ADAPTED FOR ADMINISTRATIVE, COMMERCIAL, FINANCIAL, MANAGERIAL OR SUPERVISORY PURPOSES, NOT OTHERWISE PROVIDED FOR
    • G06Q20/00—Payment architectures, schemes or protocols
    • G06Q20/38—Payment protocols; Details thereof
    • G06Q20/382—Payment protocols; Details thereof insuring higher security of transaction
    • G06Q20/3829—Payment protocols; Details thereof insuring higher security of transaction involving key management
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06Q—INFORMATION AND COMMUNICATION TECHNOLOGY [ICT] SPECIALLY ADAPTED FOR ADMINISTRATIVE, COMMERCIAL, FINANCIAL, MANAGERIAL OR SUPERVISORY PURPOSES; SYSTEMS OR METHODS SPECIALLY ADAPTED FOR ADMINISTRATIVE, COMMERCIAL, FINANCIAL, MANAGERIAL OR SUPERVISORY PURPOSES, NOT OTHERWISE PROVIDED FOR
    • G06Q20/00—Payment architectures, schemes or protocols
    • G06Q20/38—Payment protocols; Details thereof
    • G06Q20/389—Keeping log of transactions for guaranteeing non-repudiation of a transaction
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L9/00—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols
    • H04L9/08—Key distribution or management, e.g. generation, sharing or updating, of cryptographic keys or passwords
    • H04L9/0816—Key establishment, i.e. cryptographic processes or cryptographic protocols whereby a shared secret becomes available to two or more parties, for subsequent use
    • H04L9/0819—Key transport or distribution, i.e. key establishment techniques where one party creates or otherwise obtains a secret value, and securely transfers it to the other(s)
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L9/00—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols
    • H04L9/08—Key distribution or management, e.g. generation, sharing or updating, of cryptographic keys or passwords
    • H04L9/088—Usage controlling of secret information, e.g. techniques for restricting cryptographic keys to pre-authorized uses, different access levels, validity of crypto-period, different key- or password length, or different strong and weak cryptographic algorithms
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L9/00—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols
    • H04L9/08—Key distribution or management, e.g. generation, sharing or updating, of cryptographic keys or passwords
    • H04L9/0891—Revocation or update of secret information, e.g. encryption key update or rekeying
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L9/00—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols
    • H04L9/08—Key distribution or management, e.g. generation, sharing or updating, of cryptographic keys or passwords
    • H04L9/0894—Escrow, recovery or storing of secret information, e.g. secret key escrow or cryptographic key storage
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L9/00—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols
    • H04L9/12—Transmitting and receiving encryption devices synchronised or initially set up in a particular manner
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L9/00—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols
    • H04L9/32—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols including means for verifying the identity or authority of a user of the system or for message authentication, e.g. authorization, entity authentication, data integrity or data verification, non-repudiation, key authentication or verification of credentials
    • H04L9/321—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols including means for verifying the identity or authority of a user of the system or for message authentication, e.g. authorization, entity authentication, data integrity or data verification, non-repudiation, key authentication or verification of credentials involving a third party or a trusted authority
    • H04L9/3213—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols including means for verifying the identity or authority of a user of the system or for message authentication, e.g. authorization, entity authentication, data integrity or data verification, non-repudiation, key authentication or verification of credentials involving a third party or a trusted authority using tickets or tokens, e.g. Kerberos
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L2209/00—Additional information or applications relating to cryptographic mechanisms or cryptographic arrangements for secret or secure communication H04L9/00
    • H04L2209/56—Financial cryptography, e.g. electronic payment or e-cash

Definitions

  • the present disclosure relates to communication of sensitive data in a restricted data channel.
  • An extended infrastructure connects banks, merchants and cardholders through a series of different networks with a transaction scheme infrastructure mediating the authorisation of a transaction and settlement and clearing processes.
  • the transaction scheme infrastructure itself will be adapted to implement a latest version of a protocol, but particular system elements - for example, the computing hardware of a merchant processing a transaction - may not be. This may require the constraints of an older version of the protocol to be adopted - these may for example include using a limited number of data fields because of significant constraints on the transmission of data in earlier versions of a protocol.
  • an older version of a protocol may for example only be adapted to identify particular elements of a payment card in a transaction (the PAN - Primary Account Number - the expiry date, and the CVC2 code).
  • the disclosure provides a method of communicating information relating to an event using a data field, the method comprising: obtaining one or more elements of information relating to the event and determining a cryptographic record of the event using the one or more elements of information; combining some or all of each of the elements with time information associated with recordal of the event to fill a first set of places in the data field and using the cryptographic record to fill a second set of places in the data record; communicating a message including the data field, wherein a receiving the message can recover the one or more elements using the time information and can validate that the elements are correctly recovered by recalculating the cryptographic record from the recovered elements and matching the recalculated cryptographic record with the cryptographic record recovered from the data field.
  • a restricted data field can be used to communicate significant information concerning an event, with sufficient significant information being transmitted that full information can be reconstructed by the recipient, with a cryptographic record being available so that the recipient can determine that the reconstructed full information is correct. This is particularly valuable when information needs to be communicated from a first party to a second party through a protocol that does not allow for full information transfer, for example when the information needs to be transferred through a third party that only supports a limited data transfer protocol.
  • the event is a service instance, such as generation of a transaction record or transaction credentials. This may apply, for example, within a transaction scheme. Embodiments are described which relate to performance of digital transactions, and the constraint may then be that while transaction credentials may be generated and subsequently validated according to a recent protocol, the transaction data may need to pass through a channel or an entity (such as a merchant server or payment service provider) that only supports an older protocol with limited data fields.
  • a service instance such as generation of a transaction record or transaction credentials. This may apply, for example, within a transaction scheme.
  • Embodiments are described which relate to performance of digital transactions, and the constraint may then be that while transaction credentials may be generated and subsequently validated according to a recent protocol, the transaction data may need to pass through a channel or an entity (such as a merchant server or payment service provider) that only supports an older protocol with limited data fields.
  • the elements may comprise a transaction counter.
  • the elements may comprise a random or an unpredictable number.
  • the elements may comprise a key identifier - in such cases, a change in key identifier may be synchronised with a change in time information, and a key identified by the key identifier may be used to compute the cryptographic record.
  • the first set of places further comprises one or more check bits for identification of the time information.
  • This approach can be particularly beneficial in enabling the information elements to be recovered without a retry process, as it can remove the possibility of ambiguity in the time information.
  • the disclosure provides a method of obtaining information relating to an event using a data field, the method comprising: receiving a message relating to an event wherein the message includes a data field; resolving the data field into a first set of places containing combined transaction elements and a second set of places comprising a cryptographic record of the event; determining time information associated with the recordal of the event, and using the time information to establish whole or partial elements of information relating to the event that had been combined with the time information to fill the first set of places in the data field; establishing whole elements of information relating to the event from any partial elements of information relating to the event; and calculating cryptographic record data from the elements of information relating to the event and establishing the elements of information relating to the event are correct by matching the calculated cryptographic record data against the cryptographic record from the second set of places in the data field.
  • This event may be a service instance. It may, for example in the context of a transaction scheme, comprise generation of a transaction record or transaction credentials, in which case the method may further comprise validating the transaction record or transaction credentials after obtaining the information relating to the event.
  • elements may comprise a transaction counter.
  • the elements may comprise a random or an unpredictable number.
  • the elements may comprise a key identifier.
  • a change in key identifier may be synchronised with a change in time information, and a key identified by the key identifier is used to compute the cryptographic record.
  • establishing whole elements of information relating to the event from any partial elements of information relating to the event may comprises calculating the cryptographic record data and matching it against the cryptographic record from the second set of places in the data field, and if there is no match varying the time information and re-establishing whole elements of information relating to the event from any partial elements of information relating to the event using the varied time information.
  • Such a retry process enables the method to be effective even when the event may have taken place at a time during an extended time period, in which case there is a significant likelihood of ambiguity in the time information.
  • the first set of places further comprises one or more check bits for identification of the time information, and the one or more check bits are used to establish the correct time information before establishing whole or partial elements of information.
  • establishing whole elements of information relating to the event from any partial elements of information relating to the event may comprise calculating the cryptographic record data and matching it against the cryptographic record from the second set of places in the data field, and if there is no match varying one of the elements and recalculating and rematching the cryptographic record data according to a predetermined plan until there is a successful match.
  • Such a retry process allows elements to be established accurately even when severe constraints in the volume of information that can be transmitted for that element leads to potential for ambiguity.
  • the disclosure provides a computing node adapted to perform any of the method of the first aspect, the method of the second aspect, or the methods of both aspects.
  • Figure 1 shows a general approach adopted by elements of the disclosure in addressing technical problems associated with the communication of sensitive data over a restricted data channel
  • Figure 2 shows schematically a distributed transaction architecture using a four-party model
  • Figure 3 illustrates elements of a complex distributed system adapted to implement the transaction architecture of Figure 2;
  • Figure 4 shows schematically an exemplary system for enabling digital transactions in the transaction architecture of Figures 2 and 3;
  • Figure 5 illustrates an Expiry Date field as used in EMV protocols
  • Figure 6 illustrates alternative strategies for repurposing an Expiry Date field and associated validity challenges
  • FIG. 7 illustrates a general approach for generation, transport and validation of dynamic transaction data (DTD);
  • Figure 8 illustrates schematically a process for generation of dynamic transaction data in accordance with an embodiment of the disclosure
  • Figure 9 illustrates one approach to Un predictable Number generation usable in the process of Figure 8;
  • Figure 10 illustrates an alternative approach to Unpredictable Number generation usable in the process of Figure 8;
  • Figure 11 illustrates in more detail the process of Dynamic CVC generation shown in Figure 8;
  • Figure 12 illustrates schematically a process for validation of dynamic transaction data in accordance with an embodiment of the disclosure
  • Figure 13 illustrates an alternative strategy for date control by including control bits with ATC data
  • Figure 14 illustrates schematically an arrangement for a distributed system for digital enablement of transactions
  • Figure 15 illustrates a computing node of the arrangement of Figure 14 in more detail
  • Figure 16 illustrates elements within the computing node of Figure 15
  • Figure 17 illustrates an exemplary modified tokenization process for transactions using a legacy use case with the nodes of Figures 15 and 16;
  • Figure 18 illustrates a key rotation process for a system using a legacy use case
  • Figure 19 illustrates an exemplary set of cryptographic mechanisms for use for digitized transactions using a legacy use case
  • Figure 20 illustrates an approach to carry a local transaction counter using a legacy use case suitable for use with the nodes of Figures 15 and 16;
  • Figure 21 illustrates using the approach of Figure 20 in delivery of a local transaction counter using the Card Verification Code (CVC) for use with the nodes of Figures 15 and 16;
  • CVC Card Verification Code
  • Figure 22 indicates results using dynamic expiry date for the legacy use case around the end of a month for both even and odd nodes
  • Figure 23 show's consequences for node information, retry flag and key list reference in the context shown in Figure 22;
  • Figure 24 show's consequences for using key list reference to identify a key list in the context shown in Figure 22;
  • Figure 25 provides greater detail on use of key list reference to identify a key list when using a dynamic expiry date in a legacy use case in connection with begimiing and end of month issues in the context shown in Figure 22.
  • a first computing entity 1001 generates sensitive data which it washes to be available to second computing entity 1002 for validation. Communication needs however to be mediated through a third computing entity 1003, with this communication involving a restricted data channel 1004.
  • the data channel 1004 may be restricted.
  • One is that the overall amount of data that can be transmitted is limited - in this case, the data channel only contains n places for data of a particular type to be transmitted.
  • the other is that there may be constraints on the values that can be used in a particular field. In this case, x places of the total n places are constrained in the values that can be accepted.
  • information to meet security requirements is carried by repurposing original data fields.
  • data fields for static data may be reused for dynamic data which contains information for use in additional security protocols.
  • Both types of constraints create technical challenges. The limited number of places makes it difficult to convey the required amount of information.
  • Various mechanism may be used to address this. One is conveying a limited amount of information directly, but by including a check mechanism - such as a hash - to ensure that the generator and the validator are performing the same calculation on the same data.
  • the original purpose of a repurposed data field may create constraints on the values that can be used, particularly if the third computing entity 1003 continues to behave as though the original protocol is in place, and it is checking data accordingly.
  • One example of problems caused by a repurposed field is where the original field is for a date.
  • One example is in a transaction scheme, where one transaction data field is for the expiry date of the relevant payment card, represented in MMYY format.
  • the first computing entity 1001 is a payment card or other payment device
  • the second computing entity 1002 is the authoriser of the transaction (an issuing bank or transaction scheme infrastructure acting on behalf of the issuing bank)
  • the third computing entity 1003 is a merchant point of sale terminal
  • the third computing entity 1003 may be programmed to reject the potential transaction without forwarding it for authorisation if the expiry date is clearly incorrect - for example, if the month value is impossible, or the year value is too far into the future or in the past.
  • Any reuse of such a field needs to ensure that the third computing entity 1003 does not prevent the data from even passing through the restricted data channel to the second computing entity 1002.
  • This combination of constraints can provide significant technical challenges as in order to meet security requirements, dynamic data changing from event to event may be desirable, rather than static data.
  • One important security mechanism is for validity of credentials to be time limited. This requires time information in some form to be included in data transmitted from generator to validator. Length of validity of information also poses a challenge - the longer the period of validity, the more information that will typically need to be transferred, particularly if other relevant criteria - such as the cryptographic keys used for encoding - change over the validity period.
  • Embodiments of the disc losure illustrate different strategies for repurposing a limited number of fields, at least some of which are constrained, to contain dynamic data.
  • Approaches include providing least significant bit data of key variables, and by then enabling reconstruction of the full key variables from known data.
  • Approaches also include incorporation of combination of variable data with time data, and by establishment of the variable data by subtracting the time data, hi such cases, it may be possible for the recorded time value to be different from the current time value - this may happen where there is an extended validity period, and where transactions may be held before transmission or where data may be provided out of sequence. The variation in time value will then be limited, and so may be addressed by an iterative retry process or by inclusion of check data.
  • Figure 2 is a block diagram of a typical four-party model or four-party payment transaction scheme. The diagram illustrates the entities present in the model and the interactions occurring between entities operating in a card scheme.
  • card schemes - payment networks linked to payment cards - are based on one of two models: a three-party model or a four-party model (adopted by the present applicant ).
  • a three-party model or a four-party model (adopted by the present applicant ).
  • the four-party model is described in further detail below.
  • the four-party model may be used as a basis for the transaction network.
  • the model comprises four entity types: cardholder 110, merchant 120, issuer 130 and acquirer 140.
  • the cardholder 110 purchases goods or services from the merchant 120.
  • the issuer 130 is the bank or any other financial institution that issued the card to the cardholder 110.
  • the acquirer 140 provides services for card processing to the merchant 120.
  • the model also comprises a central switch 150 - interactions between the issuer 130 and the acquirer 140 are routed via the switch 150.
  • the switch 150 enables a merchant 120 associated with one particular bank acquirer 140 to accept payment transactions from a cardholder 110 associated with a different bank issuer 130.
  • a typical transaction between the entities in the four-party model can be divided into two main stages: authorisation and settlement.
  • the cardholder 110 initiates a purchase of a good or service from the merchant 120 using their card. Details of the card and the transaction are sent to the issuer 130 via the acquirer 140 and the switch 150 to authorise the transaction.
  • the cardholder 110 may have provided verification information in the transaction, and in some circumstances may be required to undergo an additional verification process to verify their identity (such as 3-D Secure in the case of an online transaction). Once the additional verification process is complete the transaction is authorized.
  • the transaction details are submitted by the merchant 120 to the acquirer 140 for settlement.
  • the transaction details are then routed to the relevant issuer 130 by the acquirer 140 via the switch 150.
  • the issuer 130 Upon receipt of these transaction details, the issuer 130 provides the settlement funds to the switch 150, which in turn forwards these funds to the merchant 120 via the acquirer 140.
  • the issuer 130 and the cardholder 110 settle the payment amount between them.
  • a service fee is paid to the acquirer 140 by the merchant 120 for each transaction, and an interchange fee is paid to the issuer 130 by the acquirer 140 in return for the settlement of funds.
  • the roles of a specific party may involve multiple elements acting together. This is typically the case in implementations that have developed beyond a contact-based interaction between a customer card and a merchant terminal to digital implementations using proxy or virtual cards on user computing devices such as a smart phone.
  • Figure 3 shows an architecture according to an embodiment of the disclosure appropriate for interaction between a cardholder and a merchant.
  • This Figure shows a general-purpose architecture for reference, but it shows elements of an architecture used when a cardholder carries out an online transaction with a merchant server.
  • a cardholder will use their payment card 6 - or a mobile computing device such as smartphone 11 adapted for use as a contactless payment device - to transact with a POS terminal 7 of a merchant 2.
  • the cardholder will use his or her computing device which may be any or all of a cellular telephone handset, a tablet, a laptop, a static personal computer or any other suitable computing device (here cellular telephone handset or smartphone 11 is shown) - and other computing devices such as a smart watch or other wearable device may also be used) - to act either as a proxy for a physical payment card 6 or as a virtual payment card operating only in a digital domain.
  • the smartphone 11 may achieve this with a mobile payment application and a digital wallet, as described below.
  • the smart phone 11 can use this to transact with a merchant POS terminal 7 using NFC or another contactless technology, or to make a payment in association with its wallet service as discussed below.
  • online transactions with a merchant are of particular interest in connection with embodiments of the disclosure, rather than contact or contactless transactions with a merchant POS terminal 7.
  • the smartphone 11 may also be able to interact with a merchant serv er 12 representing the merchant 2 over any appropriate network connection, such as the public internet - the connection to the merchant may be provided by an app or application on the computing device.
  • the transaction scheme infrastructure (transaction infrastructure) 5 here provides not only the computing infrastructure necessary to operate the card scheme and provide routing of transactions and other messaging to parties such as the acquirer 3 and the issuer 4, but also a wallet service 17 to support a digital wallet on the cardholder computing device, and an internet gateway 18 to accept internet based transactions for processing by the transaction infrastructure.
  • the wallet service 17 may be provided similarly by a third party with an appropriate trust relationship with the transaction scheme provider.
  • a token sendee provider 19 is present (again, this is shown as part of transaction infrastructure 5 but may be provided by a third party with appropriate trust relationships), and the transaction scheme infrastructure provides a digital enablement service 16 to support the performance of tokenized digital transactions, and to interact with other elements of the system to allow transactions to be performed correctly - this digital enablement service may include other elements, such as token service provision.
  • the transaction is validated in the transaction scheme by mapping the cardholder token to their card PAN, checking the status of the token (to ensure that it is in date and otherwise valid) and any customer verification approach used. This allows the issuer to authorise the transaction in the normal manner.
  • FIG. 4 shows elements of a transaction infrastructure to support digitized payments from a mobile device in more detail.
  • This Figure shows as a specific example the applicant's Mastercard Cloud-Based Payment (MCBP) architecture - this is exemplary rather than specific to the invention, and illustrates how the architecture is used to support a mobile payment application 215 on a mobile device (such as smartphone 11) - here the mobile payment application 215 is shown as contained within a wallet application or digital wallet 41.
  • a digital wallet 41 may communicate with a wallet server 17 to allow management of the mobile payment application, and it also can be used to request digitization of a payment card 6 to be used by the mobile device 11.
  • the Mastercard Digital Enablement Service (MDES) 42 performs a variety of functions to support mobile payments and digitized transactions. As indicated above, the MDES 42 is exemplary only - other embodiments may use digitization, tokenization and provisioning services associated with other transaction processing infrastructures, for example.
  • the wallet server 17 is not a part of the MDES 42 - and need not be present, for example if the mobile payment application 215 is not embedded within a digital wallet 41 - but acts as an interface between the mobile device 11 and the MDES 42.
  • the MDES 42 also mediates tokenized transactions so that they can be processed through the transaction scheme as for conventional card transactions.
  • the following functional elements shown within the MDES 42 the Account Enablement System (AES) 43, the Credentials Management System (CMS) 44, the Token Vault 45, and the Transaction Management System (TMS) 46. These will be described briefly below.
  • the Account Enablement System (AES) 43 is used in card digitisation and user establishment. It will interact with the mobile payment application (here through the wallet server 17) for card digitisation requests and will populate the Token Vault 45 on tokenization and will interact with the CMS 44 to establish a card profile with associated keys for digital use of the card.
  • AES Account Enablement System
  • the Credentials Management System (CMS) 44 supports management of cardholder credentials and is a key system within the MDES 42.
  • the core system 441 manages synchronisation with the transaction system as a whole through interaction with the TMS 46 and manages the channel to the AES 43.
  • the dedicated system 442 provides delivery of necessary elements to the mobile payment application such as the digitized card and credentials and keys in the form needed for use. This system may also interact with the wallet server 17 for management of the mobile payment application.
  • the Token Vault 45 - which is shown here as within the MDES 42, but which may be a separate element under separate control - is the repository for token information including the correspondence between a token and the associated card.
  • the MDES 42 will reference the Token Vault 45, and tokenization of a card will result in creation of a new entry in the Token Vault 45.
  • TMS 46 Transaction Management System 46 is used when processing tokenized transactions. If a transaction is identified by the transaction scheme as being tokenized, it is routed to the TMS 46 which detokenizes the transaction by using the Token Vault 45. The detokenized transaction is then routed to the issuer (here represented by Financial Authorisation System 47) for authorisation in the conventional manner.
  • the TMS 46 also interacts with the CMS 44 to ensure synchronisation in relation to the cardholder account and credentials.
  • Embodiments of the disclosure may be performed using the architecture shown in Figures 3 and 4.
  • digital transactions such as those made in online commerce are of particular interest.
  • a consumer will typically be interacting with a merchant server through a website over the browser (or a specific app) on the user's computing device.
  • the user will use their credit card for a transaction, but the card will not be present and the consumer is here not transacting through a payment application on their own computing device but is using the payment card in a manner similar to a conventional “cardholder not present” (CNP) transaction, in which the merchant receives specific details of the payment card, but will not receive an application cryptogram generated by the payment card itself, or by a payment application on a user computing device.
  • CNP cardholder not present
  • a possible limitation is that a system entity such as the merchant server - or a payment service provider gateway supporting the merchant - may be operating under an old protocol version, and so will only be able to support very limited provision of payment card data.
  • An approach to managing the provision of dynamic data using limited data fields allowed by older protocol versions is described with reference to Figures 5 to 12.
  • This approach relates to performance of digital transaction using a transaction scheme, and it is applicable to online payment as described above - it has particular relevance to online commerce, and in particular to Secure Remote Commerce (SRC - htps://www.emvco.com/emv-technologies/src/), which is a set of specifications developed by or for EMVCo that provide a secure approach to the processing of e-commerce transactions.
  • a transaction may be identified by Dynamic Token Data (DTD), where the transaction is performed using a token (managed by an architecture as shown in Figures 3 and 4) rather than a PAN and content is varied with each transaction.
  • DTD Dynamic Token Data
  • Cardholder authentication is performed using a separate mechanism, 3DS (a version of 3-D Secure, discussed for example at https://en.wikipedia.org/wiki/3-D Secure, suitable for use for cardholder authentication in Card Not Present (CNP) transactions).
  • 3DS a version of 3-D Secure, discussed for example at https://en.wikipedia.org/wiki/3-D Secure, suitable for use for cardholder authentication in Card Not Present (CNP) transactions.
  • the DTD data needs therefore to be sufficient to identify the transaction and to allow an authoriser to determine that the transaction is legitimate, and it is desirable for DTD data generation to be independent of the 3DS process (preferably so that this could be done either before or after any call to the 3DS process).
  • DTD data should be such that the content varies with each transaction but that there is a clear binding to the relevant token used, and while the data does not need to be an EMV cryptogram of an existing type it needs to be such that legitimacy of the transaction can be verified.
  • Dynamic Token Data - in particular, of Dynamic Expiry Date and Dynamic CVC forming part of Dynamic Token Data - will now be described, as will processes for generation and validation of these values in the context of a Secure Remote Commerce transaction. It should be noted that this approach is applicable to any product or service using a tokenized transaction and is not limited to SRC, and that where reference is made to SRC transactions below the person skilled in the art will appreciate that there is no intention to limit the use of the functionality described to the context of an SRC transaction.
  • Expiry Date comprises four values in the form YYMM, with YY used to carry “year” information (YY being a two-digit value between 00 and 99) and MM used to carry “month” information (MM being a two-digit value between 01 and 12).
  • YY used to carry “year” information
  • MM used to carry “month” information
  • An intermediary computing system using a legacy version of the protocol - a Payment Service Provider or a merchant server - may invalidate a transaction if the Expiry Date value appears to be invalid or impossible. This poses a significant restraint on the dynamic data that can be carried in this field - the dynamic data must correspond to a possible date, this date must not be in the past, but it must also not be too far into the future to be credible. If 6 bits of data are carried, this would require date values to be up to 5-6 years into the future - these should not be rejected by legacy systems.
  • ATC Application Transaction Counter
  • UN Unpredictable Number
  • the Unpredictable Number is a value used to provide variability and uniqueness in cryptogram generation - different methods of UN generation are possible, with the overall size of the UN and the unlikelihood of the process to generate it being replicated by an attacker being the main factors in security.
  • the ATC and UN values are used to generate a cryptogram in a DTD transaction, and are recovered by the entity responsible for validation of the dynamic token data.
  • a preferred choice is for 3 bits to be allocated to the ATC and 3 bits to the UN.
  • the next best choice is for 2 bits to be allocated to the ATC and 4 bits to the UN - it is however felt that the consequent increase in security of the UN is outweighed by the risk of errors in processing a basket of goods or services from several merchants, as this may involve the very rapid performance of a number of transactions and may cycle the ATC value if only 2 bits are used.
  • CVC2 the Card Security Code
  • CVC2 the Card Security Code
  • DTD generation, transport and validation processes will now be described with reference to Figure 7.
  • the relevant computing entities are adapted to perform current versions of EM V protocols and are aware of and adapted to perform the relevant DTD process functions.
  • the transport process it is necessary for the transport of DTD related data not to impact any transport of EMV transaction data and/or 3DS transaction data if the latter is used as part of the transaction flow.
  • the DTD generation process is described in detail below with reference to Figure 8.
  • the generator has access to information from the card profile: here, the relevant data is the PAN (or Token), referred to here as didToken: and the initial vector (IV) used for DTD transactions ivCvcTrackDtd.
  • the initial vector can be generated using a cryptographic operation over a list of data containing for example some identification of the token such as defined when using track data including PAN, Service Code, Static Expiry Date and so on.
  • the generator will also be able to provide unique transaction credentials for the DTD transaction: the ATC didATC; and a session key SK.
  • an Epoch Time value is obtained 201.
  • the initial value obtained is the Unix Epoch Time when Dynamic Token Data generation is initiated - here dtdGenUET. This is the number of seconds elapsed since midnight (UTC) on January 1, 1970, ignoring leap seconds.
  • This value is adjusted by an appropriate ratio to provide a value dtdAdjGenUET and a reference time is obtained by using modulo 100000 of the adjusted Unix Epoch Time to provide a value dtdRefTimeGenUET.
  • the Card Profile data needed is obtained 202 - this comprises the value of the PAN/Token dtdToken and the value of the ATC of the session key (SK) to be used to generate the DTD Dynamic CVC, did ATC.
  • the relevant part of the ATC is then extracted and reformatted 203.
  • dtdLSbATCBin The n least significant bits (rightmost) of the ATC are extracted as dtdLSbATCBin , with n defined by the parameter dynamicExpiryDateNbrATCBits. This value dtdLSbATCBin is then converted to a decimal value dtdLSbATCNum.
  • the next step is to generate 204 a time-based unpredictable number.
  • Buffer dtdToken
  • This buffer is then hashed using SHA256 to form dtdGenHash, after which the buffer is wiped. Other choices could be made for the hash - for example, SHA512 could be used rather than SHA256, or another hashing mechanism such as SM3 could be used.
  • the three least significant bits of the hash are extracted as dtdLSBGenHash and converted to a numerical value dtdLSBGenHashNum. This is then converted to a modulo 100000 value dtdLSBGenHashNumMod and the time-based unpredictable number is calculated by adding this value to the time value module 100000.
  • dtdGenUN (dtdRefTimeGenUET + dtdGenHashNumMod) MOD 1000000
  • a number of variations are possible in generating the Unpredictable Number, as shown in Figures 9 and 10 - these show other approaches which both take a different form of the UTC date, but which take two different approaches to including ATC data.
  • a Y byte buffer is constructed from a 4-byte BCD (binary coded decimal) UTC date - in this case, in YYYYMMDD format - and appropriate PAN and ATC contributions.
  • the PAN is provided as an n digit value, padded if necessary, from which an X byte BCD value is formed.
  • the approach to providing an ATC value differs, however: in the first case shown in Figure 9, the full ATC value is used and provided as a 2-byte hexadecimal value, whereas in the second case shown in Figure 10, the least significant 4 bits are provided and form a 1-byte hexadecimal value.
  • dtdGenNbrMonthsBin dtdLSbATCBin
  • dtdRefTimeGenUETBm This binary value is then converted to a numerical value dtdGenNbrMonths .
  • the next month is identified using dtdGenUET , and expressed as a value dtgGenYYMM Next, which is dtdGenYYMM + 1.
  • the Dynamic Expiry Date will appear to be legacy processors to be a valid Expiry Date, as it has the correct format, does not lie in the past, and does not lie too far into the future.
  • the next step is to generate 206 the DTD Dynamic CVC.
  • This process is also shown in Figure 11.
  • An 8-byte input buffer is formed from the concatenation of the IV value ivCvcTrackDtd, the 4-byte time-based UN did Gen UN and the 2-byte ATC value dtdATC.
  • the dynamic CVC value is then computed cryptographically from the buffer using the session key SK by an appropriate cryptographic process, such as DES3 (a 2-key Triple DES Encryption (EDE) using ECB mode), with the three least significant digits of the 8-byte result, expressed in decimal, used as the CVC.
  • DES3 a 2-key Triple DES Encryption (EDE) using ECB mode
  • the buffer can be wiped once the Dynamic CVC value has been created.
  • the ATC value and the session key can be wiped 207, and the DTD values delivered 208 to the merchant (and so to the acquirer) as transaction data for use in an online authorization request for the transaction: a PAN (Token) value dtdToken, an Expiry Date value using DTD Dynamic Expiry Date dtdDynamicExpiryDate, and CVC2 using DTD Dynamic CVC dtdDynamicCVC.
  • a PAN (Token) value dtdToken an Expiry Date value using DTD Dynamic Expiry Date dtdDynamicExpiryDate
  • CVC2 DTD Dynamic CVC dtdDynamicCVC
  • the transport process is straightforward, as all transaction data has the format of legacy transaction data. If the merchant or the acquirer or any associated system entity (such as the merchant's payment service provider (PSP)) is only adapted to use legacy versions of the protocol, this will not affect the routing of the transaction data from the merchant to the acquirer to the transaction scheme for authorisation. At this point, the dynamic token data needs to be validated.
  • PSP payment service provider
  • the validator will have access to various information, and also to a HSM (Hardware Security Module) capable of performing necessary cryptographic computation. Specifically, these resources are as follows.
  • the validator has access to the following information associated with the PAN(Token): o Cryptographic Keys such as the Issuer Master Key: IMK o Last known ATC: dtdLastKnownATC o Information to construct the Track data (trackDtd) that will be used to generate the IV value ( ivCvcTrackDtd ) using the following values:
  • trackDtdServiceCode “yyy” value in “trackDtd”
  • trackDtdPanSequenceNumber “z” value in "trackDtd”
  • the ( trackDtd ) is a 19-byte value: " ⁇ PAN>Dxxxxyyyz00000000F” with ⁇ PAN> set to dtdToken, D defined as a delimiter and “000000000000F” defined as a filler.
  • the validator has access to the following list of parameters: o Any optional additional data shared between the “generator” and the “validator”: dtdAdditionalData (may be unused in a simplified version) o Number of bits of ATC carried using Dynamic Expiry Date: dynamicExpiryDateNbrATCBits (may be set to 3 in simplified version) o Number of bits of time-based UN carried using Dynamic Expiry Date: dynamicExpiryDateNbrUNBits (may be set to 3 in simplified version) o Threshold for adjustment (up) of Expiry Date in case of failure of DTD Validation: dtdMonthShifiUpThreshold , a value hh:mm:ss PM expressed using GMT timezone (eg 11:55:00 PM GMT) o Threshold for adjustment (down) of Expity Date in case of failure of DTD Validation: dtdMonthShiftDownThreshold , a value hh:mm:
  • the HSM is able to generate a Card Master Key (CMK) and Session Key (SK) from the Issuer Master Key (IMK), to generate the IV from track data as indicated above and the Card Master Key (CMK), and to use the Session Key SK, IV, UN and ATC for CVC Validation.
  • CMK Card Master Key
  • SK Session Key
  • time information must be obtained 401. This can be carried out in exactly the same way as for the generator, as exactly the same information is available.
  • the PAN(Token) value can simply be extracted 402 from the transaction data as dtdToken.
  • the IV value can also be reconstructed 403 from the DTD transaction data, as this contains everything needed to reconstruct the Track data ( trackDtd) used to generate the IV value ( ivCvcTrackDtd ).
  • trackDtd is a 19-byte value
  • ⁇ PAN>Dxxxxyyyz000000000000F used to identify the token being used for the transaction with xxxx being trackDtdExpiryDate (a static value that is not linked to the dynamic expiry date used in the context of DTD transactions), yyy trackDtdServiceCode (a static value used in legacy system to qualify the supported services for a transaction) and z trackDtdPANSequenceNumber (a static value that can be used to identify several cards sharing the same PAN value).
  • the next step is special to the validation process, and involves setting 404 the month shift value, which may be 0 (the default), 1 or -1.
  • the first part of this is to establish the next month value dtdValYYMMNext by adding one to the current time dtdValYYMM, which is the YYMM format of dtdValUET.
  • the DTD Dynamic Expiry Date ( dtdDynamicExpiryDate is then retrieved from DTD transaction data, and the next month value is subtracted from this to give the number of months computed by the generator - dtdGenNbrMonths .
  • the next step is to try to establish whether the month shift value is correct, which is determined by establishing whether or not the DTD Dynamic CVC can be validated, as discussed further below.
  • the number of months is converted to a binary value ( dtdGenNbrMonthsBin ) and available ATC and UN information is extracted 405 from the DTD Dynamic Expiry date - the n most significant bits of dtdGenNbrMonthsBin form the n least significant bits of the ATC dtdLSbATCBin , and the m least significant bits of dtdGenNbrMonthsBin form the m least significant bits of the reference time dtdRefTimeGenUETBin, where n is defined by dynamicExpUyDateNbrATCBits and m is defined by dynamicExpiryDateNbrUNBits .
  • the next step after this is to construct 406 an ATC candidate from this data. This is done by retrieving the last known ATC value dtdLastKnownATC for that PAN(Token) dtdToken , which the validator will have access to through previous validation processes. The last known ATC value and the retrieved ATC information from the Dynamic Expiry Date will be used together to reconstruct the candidate ATC value dtdCandidateATC, typically the lowest value consistent with the ATC information from the Dynamic Expiry Date but higher than the last known ATC value. Thi s is then converted to a decimal value dtdLSBATCNum.
  • the relevant elements are all available to recover 407 the time-based UN by replicating the process used to create it. As before, a temporary buffer is created of the token value and the relevant part of the ATC:
  • Buffer dtdToken
  • dtdAdditionalData is non-zero
  • this may be appended to the right of the buffer - padding may also be used to make the length of the buffer even.
  • This buffer is then hashed using SHA256 to form dtdValHash , after which the buffer is wiped.
  • the three least significant bits of dtdValHash are extracted as dtdLSBValHash and converted to a numerical value dtdLSBValHashNum. This is then expressed in modulo 100000 as dtdLSBValHashNumMod.
  • dtdCandidateUN 1 dtdCandidateUN” -2” and dtdCandidateUN” + 1 have the following values:
  • the next step is to compute the deltas between the reference time for validation of Dynamic Token Data and the list of candidates for UN reconstruction as above:
  • Times will then be ranked, with “past” times ranked over “future” ones
  • the next step is to attempt to validate 408 the DTD Dynamic CVC.
  • the DTD Dynamic CVC is validated using a cryptographic function that compares the supplied Dynamic CVC against a computed CVC value using an 8- byte buffer created with the concatenation of ivCvcTrackDtd, dtdRecoveredUN and dtdCandidateATC.
  • computedCVC LSD(3,Byte2Dec(LSB(2, DES3(SK) [buffer with IV, UN and
  • DES3 is a 2-key Triple DES Encryption (EDE) using ECB mode
  • LSB (n, X) is the least significant (rightmost) n bytes of byte string X
  • This validation process will succeed or fail, and this marks a decision point 409. If there is a success 410, then the current candidates (for UN and ATC) can be taken to be correct. The value for dtdLastKnownATC is updated using dtdCandidateATC, , the ATC for that Session Key is marked as used, and the result of validation is reported (as a success). If there is a failure, there is a retry process according to the following criteria:
  • Figure 13 shows an exemplary case, in which 2 bits of data have been repurposed to provide a date control. Here, these 2 bits can be cycled between four values such that we can validate the consistency between the validation date and the recovered date information.
  • the control date value can be computed using a modulus 4 over the number of days between a baseline value and the day of the generation (or validation). It can be used to determine if the generation of the dynamic CVC was performed the same day as the validation of the supplied value or the previous day.
  • the previous day can lead to adjust the reference month, when for example the generation was performed on the last day of a month and the validation is done the first day of the following month.
  • This kind of logic is also applicable for leap years, and/or when the generation and validation is done over two years (that is generation done on the last day of a year with a validation performed on the first day of the following year).
  • decentralized architecture for digital transactions has been proposed, and this is described in the applicant’s European Patent Application No. 19178583.1. Embodiments of the disclosure may also be performed on such a decentralized architecture for performing digital transactions, involving a decentralized set of nodes each capable of credential management, as is shown in Figures 14 to 16. These decentralized nodes may perform the function of a first computing entity 1001 (in generating a credential) or a second computing entity 1002 (in validating a credential) in a system as shown in Figure 1 , with any intervening entity with a legacy constraint (such as, for example, a merchant point of sale apparatus or server) being the third computing entity 1003.
  • a legacy constraint such as, for example, a merchant point of sale apparatus or server
  • Figure 14 shows a decentralized system of computing nodes Nx, each capable of both generating G and validating V credentials. These credentials can be valid across the whole system (unless restricted to some nodes as result of on-soil regulation or the like), and in this case are associated with transactions for a set of users (clients) whose transactions are routed to that node, typically through geographic proximity.
  • Nodes provide credential generation G and credential validation V as services to clients, and need to be able to generate the credentials securely and validate them securely while they are valid at least.
  • credentials are not stored - they are generated on request and validated on the fly.
  • key management K and monitoring M can be considered as services both locally at a node and across the system, and access control AC will typically be required to allow access to a service.
  • the node 80 comprises at least one networking connection 81 to allow communication to clients 90 and other nodes 91 as well as (in this example) a central node 91a coordinating activities between one or several nodes. Communication is shown here as being through separate networks to each set of other parties - through a first network cloud 92 for connection to clients, and a second network cloud 92a for connection to other nodes within the distributed system. This reflects that these networks may be physically different, or may have different security requirements and protocols.
  • the node 80 contains a plurality of conventional servers 83 (which will contain their own processors and memories - not shown - along with other components as would normally be found in a server ) and a memory 84 containing a central database. Also comprised within the node 80 are a plurality of hardware security modules 85 (HSMs), adapted to hold cryptographic material and to perform cryptographic functions securely. Here elements within the node 80 are shown communicating by means of a bus 86.
  • HSMs hardware security modules
  • the “bus” may be, for example, comprise a dedicated network connection between a group of related data centers that allows them to provide a real-time response such that they will appear to other entities communicating with the node to be part of an integrated whole.
  • credentials are generated using keys derived according to a hierarchical process. Issuer Master Keys (IMK) are associated with a specific range of tokens, and keys for use for credentials are derived hierarchically (Card Master Keys - CMK - from IMK, and then Session Keys - SK - from CMK).
  • IMK Issuer Master Keys
  • CMK Card Master Keys
  • Session Keys - SK - from CMK Session Keys
  • This approach is used for devices, such as physical cards, but is also used for digital transactions. The number of digital transactions is increasing extremely rapidly, as opposed to device-based interactions where the growth is more consistent with resources.
  • This security model involves Issuer Master Keys (IMKs) being stored in the transaction system HSMs and used to derive Card Master Keys (CMKs) from the relevant IMK and a card PAN (Primary Account Number). These CMKs are then stored in a device (typically a Secure Element or substitute technology).
  • CMKs Card Master Keys
  • a Session Key (SK) is generated using the relevant CMK and an ATC (Application Transaction Counter) for the card/device - this is currently generated by the Credentials Management System (CMS) as shown in Figure 4.
  • CMS Credentials Management System
  • PAN is a value associated directly with an account - this is the normal (numerical) way to identify the account - the term FPAN or Funding PAN may be used to indicate a reference to an account with an issuing bank;
  • TUR or “token unique reference” is a value allowing the identification of a token without exposing any PAN value, there being a mechanism within the transaction system to determine which PAN is associated with a TUR.
  • the main purpose of the cryptographic function is to provide a guarantee - this covers both integrity of the data and authentication.
  • the transaction related data protected by a cryptographic data includes identification of a transaction and the associated token, along with an indication of any cryptographic processes used and any relevant financial data (along with any other aspect of the transaction that needs to be guaranteed). This is represented by a transaction credential - this needs to be generated G and subsequently validated V, with these processes being monitored M to ensure overall system integrity and supported by a key management system K of some kind.
  • This approach allows for decentralization of the credential system from a complex central server into a number of nodes providing services.
  • These nodes will typically be geographically distributed, but may extend over a number of data centers (for example, by use of a cloud infrastructure to achieve data sharing within a node).
  • These nodes provide services - in relation to credentials, a generation service G and a validation service V - with defined rules for access control to the sendees.
  • the merchant or PSP communicates with the generation service G to obtain credentials, which are then used in a standard authorisation process, with the validating service V being called upon where necessary to validate the credential.
  • These sendees have access to the computing infrastructure (HSMs, databases) of a node.
  • Monitoring M and key management K services are also provided - these may be centrally organized or comprise a mix of coordinated and local functionality. All these services and their interrelationship are described in greater detail below.
  • This distributed approach may be supported by replacing the binding of a token to a specific hierarchically derived key, allowing instead the first available key from a stack of keys to be allocated to a tokenized transaction.
  • This approach using flexible and dynamic key management, allows for a scalable solution. Monitoring can be carried out in such a way as to ensure that the distributed architecture is secure without requiring the transmission or replication of large quantities of sensitive information.
  • This approach can also be carried out in a standard HSM using fully FIPS compliant processes - for example, DES and 3DES need not be used.
  • This approach is described in more detail in the applicant's European Patent Application No. 19178583.1. This describes how a limited number of keys can be allocated to a node while providing a deterministic process in order to pick a key to generate credentials. The same process can be used by a validation entity to determine the key that was used by the generator so that it can validate any cryptographic material that is part of the credentials submitted for validation.
  • the HSMs contain keys that are each uniquely identified by a set of key identifiers (Keyld).
  • Keyld may be a label, a value, an explicitly unique value such as a UUID, or anything else with appropriate properties.
  • These Keylds are stored in uniquely identified (Identifier) key lists - these key lists provide a list of relationships between an identifier (Id) and a stored key (Keyld).
  • the identifiers (Id) are what will be determined by the deterministic process in order to establish what key is to be used, as will be described further below.
  • each key list may be guaranteed using a seal (Seal) - if the key lists are provisioned from a central location, this may be applied by a trusted party associated with that central location.
  • a trusted party being a local functionality instead of a central location.
  • a node wall typically have a number of key lists available, but with only one active for generating credentials (G) at a given time - it will however generally be necessary for the validation sendee (V) to be able to access any key list that may be associated with a credential that is still valid. Key rotation in this approach is extremely straightforward - it may simply involve replacement of the active key list with another key list.
  • the specific key to be used is selected from the key list by the deterministic process - this will typically give a different result after key rotation, but this is not inevitably the case.
  • the generation services G do not need Key List A after key rotation, the validation services V still do - they require access to any key list that relates to a potentially valid credential.
  • the validation services V must be able to establish exactly which key was used to generate a credential by the generation services G in order to validate a credential.
  • the transaction related data to be protected cryptographically includes identification of the token associated with the transaction, but also identification of the transaction itself. For this, some kind of transaction identifier is required.
  • the credential generation and validation services have access to a local database which can be used to manage such data.
  • any generation of transaction credentials for a given token should be associated with a unique transaction identifier for each transaction. This may be a UUID, but as indicated previously, it is challenging to establish a UUID in a distributed system where identification of the transaction may need to be made by one of a number of distributed nodes.
  • an appropriate identifier structure such as a concatenation of an n bit node identifier, an e bit epoch time, and a c bit local counter may be used.
  • the size of data to be carried in transaction credentials may be reduced to a few digits by use of a local transaction counter. This could simply be stored in the local database of a node and the local (rather than a global) value incremented when a local generation sendee G generates a new' token.
  • the Local Transaction Counter may therefore contribute to the effectively unique identifier structure discussed above, with the combination of node identification, time and local transaction counter used to identify transactions efficiently and uniquely.
  • Using a time-based process for key list rotation allows the LTC value to be reset at the end of a time period without loss of these properties while limiting the size of data required to carry the LTC value as part of the transaction flow.
  • CVC2 is a static field - provided as a three digit value on the rear of a physical payment card - used to confirm knowledge of the card, rather than just the PAN.
  • This is significant as a validation service V must be able to access all the data used by a generation service G to generate a cryptogram - this will include the following: dynamic information carried as part of the transaction flow; shared information from one of the following: replicated processes (such as management of the key lists); system parameters for particular use cases.
  • the legacy transaction use case is of particular interest for embodiments of the disclosure. This provides a solution when the Merchant and/or the PSP are only able to manage PAN, Expiry Date and CVC2 as part of the transaction flow, and do not have access to additional data fields provided by more recent developments.
  • a challenge involved is in effectively identifying in a transaction how credentials have been generated in order to enable their subsequent validation - in particular, identification of which node generated the credential and which key list was used to do it, and the state of the local transaction counter. This is challenging, as transaction data is highly constrained, and to provide any of this information it will be necessary to change existing electronic transactions protocols (such as ISO 8583) or to repurpose existing fields.
  • PAN Primary Account Number
  • Expiry Date where some information can be carried in a condensed format
  • CVC2 condensed format
  • BINs Bank Information Numbers
  • PANs Bank Information Numbers
  • the top line shows a conventional tokenization process - an FPAN is associated with single token.
  • the token may be associated with nine PAN values for a legacy acceptance use case (bottom line), though as will be described below, for certain new formats a one to one mapping may still be used.
  • Reuse of transaction fields in the legacy case can thus be as follows.
  • 14 digits can be used for full identification of the token, with 1 digit for the counter associated to the token for a given number, and one to the Luhn number (which needs to be retained as a checksum to ensure valid numbers are used).
  • the 6 bits of the expiry date can be repurposed with x bits used to identify the node and y bits used to refer to the relevant key list for that node.
  • CVC2 provides three digits which can be used for the cryptogram.
  • the cryptogram plays a key role in protecting the integrity of the transaction - successful validation of a cryptogram computed over a given set of data using a correct key confirms that data originally used in credential generation is genuine. Any failure in the validation process can come from the use of wrong cryptographic material and/or corrupted transaction data.
  • each generation (G) and validation (V) service has access to a local database. Any generation of transaction credentials for a given token is associated to a unique transaction identifier for each transaction.
  • the local transaction counter (LTC) is managed by “G” for a given token in a given node using a given key list associated to a given use case. The same process applies at the time of validation by “V”. This information can be carried in the PAN field (digit 15, or digits 14 and 15) as shown in Figure 20 or using the CVC2 field as shown in Figure 21 with a retry flag in the expiry date field, with a “full counter” generated if necessary if LTC is at a higher value.
  • HMAC is chosen as the cryptographic function as this allow the use of general purpose HSMs while delivering effective functionality.
  • Identification of the token uses the PAN value. Identification of the transaction takes information from the expiry date (ISO 8583 field DEM) - specifically the node identifier and the reference, possibly also with a retry flag - and from the PAN field, which holds the local transaction counter. Identification of the key and the cryptographic method is provided from the local transaction counter (which establishes which key is chosen from the key list) together with information shared by the key management system in the key lists.
  • a variety of fields defining the transaction may be used as financial data to be used to generate the cryptogram (as shown in Figure 18), with all these fields used to generate the cryptogram, which is then decimalized and the three least significant digits used in the CVC2 field.
  • the code may be selected by any value known by both the G and V services - for example, the Luhn number of the PAN.
  • a new key list may then use a completely different coding table, making the process significantly dynamic.
  • the PAN digits identify the token and also provide a Luhn number, and the Luhn number is used to determine the ordering of digits for the CVC2 field - in this case, option 3 is chosen, indicating the least significant digit and next least significant digit of the cryptogram in the first two places, with the least significant digit of the counter in the third place. This results in a CVC2 output that can be derived by both the G and V services.
  • the Local Transaction Counter (LTC) in embodiments of the disclosure can be used for a number of functions. As indicated above, the LTC contributes to provision of a unique identifier for transactions.
  • the LTC itself is not unique, but when combined with other values - for example node identifier and time period identifier as described above, but also potentially other values such as key list identifier and PAN/TUR - it many provide a unique identifier, in particular a unique identifier for a transaction performed using a given node with a given key list for a given PAN/TUR.
  • the LTC can also be used to provide a deterministic means to select a key from a key list for cryptogram generation and validation.
  • the LTC can be used in connection with tracking of various activities relating to transactions and can provide particular benefits when only limited data can be carried in transaction fields (such as the Legacy use case discussed above).
  • a Dynamic Expiry Date field is used to carry additional information relating to LTC - the impact of Dynamic Expiry Date on the validation process is also discussed below.
  • the basic operation of the Local Transaction Counter at a generation service G and a validation service V is as follows.
  • the LTC has a key role in the performance of a service and in the recordal of a service operation in the database (dbo) of the generation service G.
  • This database is used to track individual LTC values for a given node (N i ) using a given active key list identified using keyList.Identifier.
  • An entry is created in the database when transactions are generated for the first time for a given PAN or TUR (hereafter PAN/TUR). This entry contains one LTC value only, and is updated on any subsequent generation of transaction credentials for that PAN/TUR using that given key list in that given node.
  • the credentials validation service (V) also uses a database (db v ) using LTC values of credentials that have undergone validation.
  • the database stores the list of LTC values for any given node (N i ) using a given - active - key list identified using keyList.Identifier. An entry will be created when transaction credentials are validated the first time for a given PAN/TUR using a given key list associated to a given node.
  • Each entry in the database (db v ) is associated with a list of LTC values, a list of counters (Replay, CryptoFailure and Retry - all defaulting to 0 and incremented by an appropriate event, as described below).
  • the crypto validation process as described further below will also update the content of the database (dbv) for additional purposes: detection and tracking of replays; tracking of crypto failures; and tracking the number of retries. These are described further in the applicant's European Patent Application No. 19208139.6.
  • the validation process will now be described in more detail with particular attention to LTC management issues. In this context, the validation process covers the following:
  • the legacy use case (L) is significantly more complex because of the problems caused by the limited availability of space to capture LTC and other data, as it is indicated above with reference to Figures 18 to 21.
  • the legacy use case (L) has severe size restrictions on the data that can be carried as part of transaction data, and only a part of the LTC value can be carried - typically one digit (C). This means that a recovery process has to be employed to recover LTC data effectively and reliably.
  • Validation processes are described further in European Patent Application No. 19208139.6. as mentioned above.
  • the Legacy (L) use case is complicated by the lack of space available to carry LTC data in a transaction.
  • a particular issue is that of the use of Dynamic Expiry Date and its consequences, particularly the difficulty of managing the end of the month where certain fields that can be effectively repurposed at other times become significant.
  • the following discussion relates to the use of a "Dynamic Expiry Date" to carry information in the legacy (L) use case.
  • the expiry date field is used to carry a 6-bit value (exp) by adding exp months to a next month value (YYMM) computed using t x (UTC) as the reference.
  • the dynamic expiry date is computed by G as part of the generation of transaction credentials for the “L” use case - it is used here because PAN, Expiry Date and CVC2 is the minimal set of data that can handled by a merchant/PSP and their acquirer, so some mechanism is required to carry additional necessary information.
  • Time t G can be converted to the UTC time zone, which can be used as a reference for the whole system
  • the dynamic expiry date is the combination of “next month” with a value corresponding to the 6 bits of information as described above.
  • the validation service V follows the same logic but using as a reference time tv corresponding to the validation of transaction credentials.
  • Another edge case is having a validation time prior to the generation time. We expect G and V in the same node or across nodes to use a reliable source of information for time minimizing that risk.
  • Monitoring can be also impacted, with false reporting of system misuse while the root cause was only that transaction credentials had been generated on the last day of the month and validated the following day.
  • Figure 22 provides some examples of generation of transaction credentials at the end of the month with validation the same day or on the first of the following month. Examples are also provided for generation done on the first day of the month with validation done the same day or the following day.
  • Figure 23 shows a list of values indicating the impact of a delta between the value defined by G at time to and carried using a dynamic expiry date and the value retrieved by V at time tv using a “next month” value that is shifted (i.e. one additional month) compared to what was actually used by G.
  • KR key list reference
  • a key list needs to have a limited lifetime. This is particularly necessary for the legacy use case as there is counter information that can only be carried using one digit. This does mean that some rotation of the key list (and its associated key list reference) must happen in order to reset the LTC.
  • Figure 25 describes a solution involving rotation of key lists around the end of the month. It also show's that validation of transaction credentials can be done up to 24 hours after their generation.
  • KR key list reference
  • V determines if there is a need to adjust the time used for recovery of the information carried using the dynamic expiry date:
  • Node 0 would require a bespoke process as the recovered key list reference may be corrupted following the use of a wrong “next month” value. In order to avoid any such complex process it may in practice be simplest to exclude the use of node 0 when using the legacy use case.

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Abstract

Selon la présente invention, des procédés de communication et d'obtention d'informations, dans lesquels des éléments d'informations se rapportant à un événement sont obtenus et utilisés pour définir un enregistrement cryptographique d'un événement. Le premier ensemble d'emplacements dans le champ de données est rempli d'une combinaison d'éléments conjointement avec des informations temporelles relatives à un événement. L'enregistrement cryptographique est utilisé pour remplir le second ensemble d'emplacements dans l'enregistrement de données. Lors de la réception d'un message comprenant un champ de données, le champ de données peut être divisé en un premier et un second ensemble d'emplacements. Les informations temporelles associées à l'événement peuvent ensuite être identifiées et utilisées pour identifier les éléments d'informations qui ont été combinés avec les informations temporelles pour remplir le premier ensemble d'emplacements.
PCT/US2021/018344 2020-02-26 2021-02-17 Communication de données sensibles dans un canal de données restreint WO2021173396A1 (fr)

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EP4175216A1 (fr) * 2021-10-26 2023-05-03 Mastercard International Incorporated Opérations cryptographiques et communication de données à l'aide d'un canal de données restreint
GB2612349A (en) * 2021-10-29 2023-05-03 Mastercard International Inc Transaction key generation

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EP2189934A2 (fr) * 1997-12-22 2010-05-26 Motorola, Inc. Système de messagerie sécurisée et procédé pour réaliser une transaction financière dans celui-ci
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US6434238B1 (en) * 1994-01-11 2002-08-13 Infospace, Inc. Multi-purpose transaction card system
EP2189934A2 (fr) * 1997-12-22 2010-05-26 Motorola, Inc. Système de messagerie sécurisée et procédé pour réaliser une transaction financière dans celui-ci
US7027773B1 (en) * 1999-05-28 2006-04-11 Afx Technology Group International, Inc. On/off keying node-to-node messaging transceiver network with dynamic routing and configuring
US9774401B1 (en) * 2013-07-15 2017-09-26 Paul Borrill Entangled links, transactions and trees for distributed computing systems

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